[quote]but is there any exception to a steam account no longer existing?[/quote] No, there are no exceptions being made at all by Bungie. Even prior to the unlinking change being implemented, Bungie were not unlinking accounts on players behalf regardless of the reason it was needed. Edit: just to add, even if it was possible for Bungie to unlink the account so you could link your Steam - you'd lose all progress you've gained as that's permanently bound to your linked Steam account.